2. Energy flow in ecosystems
Section 3.3
Energy flow in ecosystems

3. How does energy move through an ecosystem?
Energy flows like a one way stream in an ecosystem

4. Food chains
Steps by which energy is transferred - through eating!

5. Aquatic food chains Often start with phytoplankton and algae
In this chain, the top carnivore is 4 steps removed from the primary producer

6. Food webs
Often there are many links between different food chains

7. Decomposers and detritivores
Detritivores and decomposers are as important as other consumers
Provide a food sauce for other primary consumers
Release nutrients
Without decomposers nutrients stay locked up in dead organisms

8. Why might scientists use models such as food chains or a food web
Why might scientists use models such as food chains or a food web? What kind of predictions can be made?
Unethical to experiment on animals
Feeding relationships can be difficult to observe
A Food web can be used to predict what might happen if a particular species increases or decreases in number.

9. Disturbing a food web
Algae for krill grow beneath Antarctic sea ice? What effect might global warming have?

10. Trophic levels
Each step in a food chain or food web is called a trophic level
Primary producers are always first trophic levels
Displayed in ecological pyramids

11. Pyramid of energy
Only a small portion of energy will move from one trophic level to another

12. Pyramid of biomass
Illustrates the relative amount of of living organic matter available at each trophic level
Biomass is measured by grams of organic matter per unit area

13. Pyramid of numbers
Often a very similar shape to pyramid of biomass, but this is not always the case…